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/*
* MIT License
*
* Copyright (c) 2020 Joey Castillo
* Copyright (c) 2023 Edward Shin
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "watch_private_cdc.h"
#include <stddef.h>
#include "watch_utility.h"
#include "tusb.h"
/*
* Implement a circular buffer for the USB CDC Serial read buffer.
* The size of the buffer must be a power of two for this circular buffer
* implementation to work.
*/
// Size of the circular buffer. Must be a power of two.
#define CDC_WRITE_BUF_SZ (1024)
// Macro function to perform modular arithmetic on an index.
// eg. (63 + 2) & (64 - 1) -> 1
#define CDC_WRITE_BUF_IDX(x) ((x) & (CDC_WRITE_BUF_SZ - 1))
static char s_write_buf[CDC_WRITE_BUF_SZ] = {0};
static size_t s_write_buf_pos = 0;
static size_t s_write_buf_len = 0;
#define CDC_READ_BUF_SZ (256)
#define CDC_READ_BUF_IDX(x) ((x) & (CDC_READ_BUF_SZ - 1))
static char s_read_buf[CDC_READ_BUF_SZ] = {0};
static size_t s_read_buf_pos = 0;
static size_t s_read_buf_len = 0;
// Mask TC1 interrupts, preventing calls to cdc_task()
static inline void prv_critical_section_enter(void) {
NVIC_DisableIRQ(TC1_IRQn);
}
// Unmask TC1 interrupts, allowing calls to cdc_task()
static inline void prv_critical_section_exit(void) {
NVIC_EnableIRQ(TC1_IRQn);
}
int _write(int file, char *ptr, int len) {
(void) file;
if (ptr == NULL || len <= 0) {
return -1;
}
int bytes_written = 0;
prv_critical_section_enter();
for (int i = 0; i < len; i++) {
s_write_buf[s_write_buf_pos] = ptr[i];
s_write_buf_pos = CDC_WRITE_BUF_IDX(s_write_buf_pos + 1);
if (s_write_buf_len < CDC_WRITE_BUF_SZ) {
s_write_buf_len++;
}
bytes_written++;
}
prv_critical_section_exit();
return bytes_written;
}
int _read(int file, char *ptr, int len) {
(void) file;
prv_critical_section_enter();
if (ptr == NULL || len <= 0 || s_read_buf_len == 0) {
prv_critical_section_exit();
return -1;
}
// Clamp to the length of the read buffer
if ((size_t) len > s_read_buf_len) {
len = s_read_buf_len;
}
// Calculate the start of the circular buffer, and iterate from there
const size_t start_pos = CDC_READ_BUF_IDX(s_read_buf_pos - len);
for (size_t i = 0; i < (size_t) len; i++) {
const size_t idx = CDC_READ_BUF_IDX(start_pos + i);
ptr[i] = s_read_buf[idx];
s_read_buf[idx] = 0;
}
// Update circular buffer position and length
s_read_buf_len -= len;
s_read_buf_pos = CDC_READ_BUF_IDX(s_read_buf_pos - len);
prv_critical_section_exit();
return len;
}
static void prv_handle_reads(void) {
while (tud_cdc_available()) {
int c = tud_cdc_read_char();
if (c < 0) {
continue;
}
s_read_buf[s_read_buf_pos] = c;
s_read_buf_pos = CDC_READ_BUF_IDX(s_read_buf_pos + 1);
if (s_read_buf_len < CDC_READ_BUF_SZ) {
s_read_buf_len++;
}
}
}
static void prv_handle_writes(void) {
if (s_write_buf_len > 0) {
const size_t start_pos =
CDC_WRITE_BUF_IDX(s_write_buf_pos - s_write_buf_len);
for (size_t i = 0; i < (size_t) s_write_buf_len; i++) {
const size_t idx = CDC_WRITE_BUF_IDX(start_pos + i);
if (tud_cdc_available() > 0) {
// If we receive data while doing a large write, we need to
// fully service it before continuing to write, or the
// stack will crash.
prv_handle_reads();
}
if (tud_cdc_write_available()) {
tud_cdc_write(&s_write_buf[idx], 1);
}
s_write_buf[idx] = 0;
s_write_buf_len--;
}
tud_cdc_write_flush();
}
}
void cdc_task(void) {
prv_handle_reads();
prv_handle_writes();
}
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